In the field of drive systems it is of interest to minimize the effects of load changes as well as to follow an input command, in terms of either velocity or position, as close as possible in both transient and steady state and under all load conditions within the physical limitations of a system. Theoretically, both of these objectives may be achieved using a negative feedback control theory and employing an infinite gain in the loop. The problem encountered in such a case is that the system will necessarily become unstable so that, with this classical approach, no solution can be achieved. As a matter of fact, this remains a classical problem in system and control theory and practice.
An infinite disturbance rejection ratio, i.e., load independence, has been achieved employing a positive feedback as described in the U.S. Pat. application No. 07/323,630, filed November 1988 and entitled "Synthesis of Load-Independent DC Drive System" by these same two inventors N. A. Losic and Lj. Dj. Varga, and in the U.S. patent application No. 07/316,664, February 1989, by N. A. Losic and Lj. Dj. Varg entitled "Synthesis of Load-Independent AC Drive Systems" and allowed for issuance December 1989. The inventions have been generalized and included synthesis of a load-independent step motor drive systems in a copending and coassigned application by Lj. Dj. Varga and N. A. Losic, "Synthesis of Zero-Impedance Converter" filed December 1989.
Furthermore, a synthesis of drive systems of infinite disturbance rejection ratio and zero-order dynamics and without the use of position and velocity feedbacks is described in a copending and coassigned application by N. A. Losic and Lj. Dj. Varga, "Synthesis of Improved Zero-Impedance Converter", December 1989.